Unholy King - Son of Satan
A century has passed since the Demon King of Western Panthea and the Hero of the Eastern Allied Nations struck each other down. The world has calmed, and the demons have suffered much at the demise of their leader, becoming slaves to the other races.
Nyx, the son of the Demon King, wanted nothing but peace between the Demons and the Allied Nations, seeing the horror of his father and the Hero's death first hand. However, he disappeared a century ago. He nor the Holy Sword that the Hero wielded has been found. Castiel Sol on the hand is told he has the blood of the hero, and that he must take up arms against the rising power of the Demons. Their destiny is intertwined.